1. Field of the Invention
The present invention relates to an on-vehicle rotary electric machine, and, in particular, to an alternating current (AC) generator mounted on vehicles.
2. Description of the Related Art
In general, a vehicle is provided with an AC generator to power various components such as electric accessories and batteries which are mounted on the vehicle.
There are many types of AC generators including an AC generator provided with a Lundell type of rotor. That is, this type of AC generator is provided with Lundell type of unguiform magnetic poles forming a rotor and a stator arranged to face the rotor. In this AC generator, in order that magnetic flux may be transmitted surely between the stator and the magnetic poles (i.e., the rotor), there has been known the technique of placing a permanent magnet between mutually faced sides provided by two adjacent unguiform magnetic poles. The permanent magnet operates to prevent the magnetic flux from being leaked between the unguiform magnetic poles. As to this structure, it is significant to prevent each permanent magnet from dropping out outwardly in the radial direction of the generator due to the centurial force generated when the generator is in operation, whereby preventing the drop results in prevention of the breakage of the permanent magnets in the generator. Practically, this kind of structure has been proposed by the references such as Japanese Patent Laid-open publications. No. 7-123664, 2003-339141, and 2002-262530.
Of these, the first reference No. 7-123664 provides a structure for holding permanent magnets by resin-made holding members. The second reference No. 2003-339141 provides a structure in which magnet holding members each formed into a plate-like member made of non-magnetic material are used to enclose each permanent magnet in the axial direction of the generator.
Further, the third reference No. 2002-262530 provides a more complicated structure which uses magnet holding members and auxiliary magnetic-pole members. To be specific, each magnetic holding member, made of non-magnetic metal, is placed to enclose the outer and inner circumferential surfaces and both axial side surfaces of each permanent magnet. Each auxiliary magnetic-pole member, made of magnetic metal, is placed to cover both side surfaces of the each permanent magnet locating in the circumferential direction of the generator (i.e., the circumferential-side surfaces each face a circumferential-side surface of an adjacent unguiform magnetic pole in the circumferential direction). Additionally, in the third reference, a technique of welding the magnet holding member with the auxiliary magnetic-pole member into one unit is also taught.
However, it is pointed out that the conventional holding structures according to the foregoing various references are insufficient in the following points.
The holding structure provided by the first reference No. 7-123664 has a drawback that the holding members are short of strength, because the members are made of resin. Thus it is noted that the holding members may give rise to their breakage such as cracks.
In this regard, in the second reference No. 2003-339141, each permanent magnet is enclosed by the plate-like member made of non-magnetic metal, so that the strength is increased. This makes it possible to remove or alleviate a worry that the holding member itself may be broken. In this second technique, however, it is necessary to mutually joint the enclosing ends of the plate-like members, which raises labor lo hours in fabrication. Moreover, because each permanent magnet is enclosed in the axial direction of the generator, an amount of metal material used for producing the magnet holding member increases. Hence the magnet holding member proposed by the second reference will result in a rise in manufacturing cost.
The holding structure provided by the third reference 3 requires that each magnet holding member made of non-magnetic metal be welded to both auxiliary magnetic-pole members made of magnetic metal, thus raising manufacturing cost. In addition, the auxiliary magnetic-pole members are made of magnetic metal, as described above, so that the members may get rusty. Auxiliary magnetic-pole members which have been rusted badly may result in breakages thereof, with the result that permanent magnets may drop out.